I can tell you from my own knowledge that Ginsburg could be making more -- it sounds like he hasn't even started exploring advertising or in-app purchases in his app, and I've heard from many developers that those can be very helpful in the right places. But more important, Ginsburg says the satisfaction he's getting from working on the App Store is better than any monetary gain -- he just recently stepped away from a corporate job, and plans to make a go at creating apps for a full-time living.
It's cool to hear a straight story from one developer on the App Store about just how viable creating apps is. Of course, one thing Ginsburg doesn't talk about is how much work and training went into making his app -- that $20k in sales didn't just appear out of thin air. And not all developers see even his level of modest success, since there are so many apps on the store that don't even make it into the top lists. But Ginsburg is as good an example as any of the kinds of opportunities Apple has created with its App Store platform.